Many readers have asked us to replicate our browser speed tests on a Mac, to see the difference in platforms and performance. So we snagged a new MacBook Pro when nobody was looking and tested the latest browsers on it.

While this is a pretty good match to the tests we just finished on Windows, we're adding in a Firefox 4 pre-release build and the final version of Opera 10.6—which, all told, probably isn't that different from the beta, given the short time distance between them. We used the same browser testing parameters we're regularly using for Windows browsers, with a few exceptions.

In the case of cold and warm starts, and nine-tab loading, I could not find an equivalent of my favorite Windows timer, made by Rob Keir, that can stay on top of any window and be activated by a custom keyboard shortcut. If you know of such a Mac timer app with those features, by all means—tell us in the comments or by email. Instead, then, I had to rely on the Ultimate Stopwatch app for Android, made by Richard Hyndman. I used one finger to tap the "O" key to launch items with Command+O, while simultaneously tapping the timer app on my Nexus One, and tried my best to be consistent.

As for the testing platform, it's a MacBook Pro, bought the day of the latest hardware "refresh," with the specs shown at left here. It was kept plugged in for the tests, and running on a LAN cord for page loading measurements.

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One other quick thing I'm doing different this time around—I'm sharing my data. So if you wanted to see my actual testing results in numbers—to check my math, craft your own much more stylish graphs, or what have you—you can view them at this Google Docs spreadsheet. Note: Link has changed since first posting.

Now, onto the good graph-y stuff! Click any of the images below for a larger, wider view.

Boot-Up and Warm Loading—Winner: Safari 5!

It's not all that surprising that Apple's software engineers would have the best shot at getting fast start-ups and smooth integration down pat. What is surprising, though, are all the other results. Compared to the Windows results, everything's almost inverted—Chrome takes longer to start up, and Chrome beats out Firefox.

Tab Loading—Winner: Chrome!

I'd have expected Safari 5 to fare better at loading multiple tabs on a Mac than on Windows, but, alas. It did actually load the tabs after a while, though, as compared to a freeze-out on Windows. Chrome continues to be the savviest at tab loading—though there's no Internet Explorer 8 here to weird out the results.

JavaScript—Winner: Opera 10.6!

I don't entirely trust this result, or, at least, question whether it's the Dromaeo test we're using, or Opera's JavaScript coders, or a little of both. Opera 10.6 jumps from an also-ran in beta form to a miles-ahead winner in final form—unless it's just far, far faster on a Mac. This is, of course, just one test of certain benchmarks, and not a full picture. Still, beyond Opera's weird jump, Chrome, Safari, and Firefox performed at about par with their Windows counterparts.

DOM/CSS—Winner (By a Nose): Safari 5!

Safari and Opera trade places in Mac testing, while Chrome keeps pace with second place.

Memory Use (Without Extensions)—Winner: Safari 5!

One big caveat in this test is that Chrome's developers note that the browser "seriously over-reports memory usage"—it's a bug report they link right from the about:memory page we're using to fairly measure multi-process memory usage. That said, I don't think Chrome was going to knock down the far-and-away efficiency of Safari, or probably even catch up to Firefox in second place.

Memory Use (With Extensions)—Winner: Firefox 3.6.6!

We would have liked to test out a similar set of extensions on Firefox 4's pre-release, but even after using a don't-worry-about-compatibility tweak, our test build refused to let us try three of the five extensions in our testing guidelines. So we stuck with what we could test, and Firefox again performed well with five representative add-ons loaded. Many of our commenters will note that Firefox seems to leak memory over time—we're brainstorming a testing process that would fairly catch this. Suggestions? Drop them in the comments.

The Scores

We've tallied up how the six browsers performed in five tests—cold/warm starts, nine-tab load, JavaScript, DOM/CSS, and memory use—and we're posting the results here. It's not scientific, but we tried to be fair in calling winners, and granting ties when results were so close as to be negligible to the end user. Here's how these browsers fared, ordered in rank, out of a total of 30:

As many commenters have noted, these are just numbers and tests—they don't take into account standard features you may love about a browser, add-ons you can't get anywhere else, or a general good vibe you get from a certain browser. We just like to see how things stack up from an objective perspective, so we know what to expect when browser makers claim their newest build is, inevitably, the "fastest ever."

There you have it—our first batch of Mac-based browser results. As noted above, you can see the raw data for yourself, if you'd like. Come up with better graphs than ourselves? Have a suggestion for better Mac testing tools? We're all ears in the comments.